i've ran into places where i am 1 block from a lava block and i catch on fire. same has happened with water, except i hear the splash when i am in a block NEXT to water. i also have a wall of glass panes that separate the ocean from my room and i can swim in the space where the panes are.

there is a lava pit and when standing on the red concrete, you get burned but not on the white. you can swim in blocks on the N and W side of the "pool"